[PATCH] `pg_dump -Fd` doesn't check write return status...

The attached patch fixes the case when `pg_dump -Fd …` is called on a partition where write(2) fails for some reason or another. In this case, backup jobs were returning with a successful exit code even though most of the files in the dump directory were all zero length.

I haven’t tested this patch’s failure conditions but the fix seems simple enough: cfwrite() needs to have its return status checked everywhere and exit_horribly() upon any failure. In this case, callers of _WriteData() were not checking the return status and were discarding the negative return status (e.g. ENOSPC).

I made a cursory pass over the code and found one other instance where write status wasn’t being checked and also included that.

-sc